In general, a compressor is a mechanical apparatus that receives power from a power generation apparatus such as an electric motor, a turbine or the like and compresses air, refrigerant or various operation gases to raise a pressure. The compressor has been widely used in electric home appliances such as a refrigerator and an air conditioner, or in the whole industry.
The compressors are roughly classified into a reciprocating compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between a piston and a cylinder, and the piston is linearly reciprocated inside the cylinder to compress refrigerant, a rotary compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between an eccentrically-rotated roller and a cylinder, and the roller is eccentrically rotated along an inner wall of the cylinder to compress refrigerant, and a scroll compressor wherein a compression space to/from which an operation gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll, and the orbiting scroll is rotated along the fixed scroll to compress refrigerant.
Recently, a linear compressor has been actively developed among the reciprocating compressors. In the linear compressor, a piston is connected directly to a linearly-reciprocated driving motor to prevent a mechanical loss by motion conversion, improve the compression efficiency and simplify the configuration.
Normally, in the linear compressor, a piston is linearly reciprocated inside a cylinder by a linear motor in a hermetic shell so as to suck, compress and discharge refrigerant. In the linear motor, a permanent magnet is positioned between an inner stator and an outer stator, and driven to be linearly reciprocated due to a mutual electromagnetic force. Since the permanent magnet is driven in a state where it is connected to the piston, the piston is linearly reciprocated inside the cylinder to suck, compress and discharge refrigerant.
FIG. 1 is a side-sectional view illustrating a linear compressor applied with a conventional suction muffler, FIG. 2 is a side-sectional view illustrating the conventional suction muffler, and FIG. 3 is a graph showing a mass flow of refrigerant passing through the conventional suction muffler.
Referring to FIG. 1, in a conventional linear compressor 1, a piston 30 is linearly reciprocated inside a cylinder 20 by a linear motor 40 in a hermetic shell 10 so as to suck, compress and discharge refrigerant. The linear motor 40 includes an inner stator 42, an outer stator 44, and a permanent magnet 46 positioned between the inner stator 42 and the outer stator 44. The permanent magnet 46 is linearly reciprocated due to a mutual electromagnetic force. Here, since the permanent magnet 46 is driven in a state where it is connected to the piston 30, the piston 30 is linearly reciprocated inside the cylinder 20 to suck, compress and discharge refrigerant.
The linear compressor 1 further includes a frame 52, a stator cover 54 and a rear cover 56. In the linear compressor 1, the cylinder 20 can be fixed by the frame 52, or the cylinder 20 and the frame 52 can be integrally formed. A discharge valve 62 is elastically supported by an elastic member at the front of the cylinder 20, and selectively opened and closed due to a pressure of refrigerant in the cylinder 20. A discharge cap 64 and a discharge muffler 66 are installed at the front of the discharge valve 62, and fixed to the frame 52. One ends of the inner stator 42 and the outer stator 44 are supported by the frame 52, and also supported by a special member such as an O-ring of the inner stator 42 or an elevated portion of the cylinder 20. The other end of the outer stator 44 is supported by the stator cover 54. The rear cover 56 is installed on the stator cover 54, and a suction muffler 70 is positioned between the rear cover 56 and the stator cover 54.
In addition, a supporter piston 32 is coupled to the back of the position 30. Main springs 80 with respective natural frequencies are installed at the supporter piston 32 to allow the piston 30 to resonate. The main springs 80 are divided into a front spring 82 with both ends supported by the supporter piston 32 and the stator cover 54, and a rear spring 84 with both ends supported by the supporter piston 32 and the rear cover 56. Here, the main springs 80 include four front springs 82 and four rear springs 84. If a large number of main springs 80 are used, there are a lot of positional parameters that must be controlled to maintain balance during the motion of the piston 30. As a result, the manufacturing process is complicated and long, and the unit cost of manufacturing is high.
Moreover, the refrigerant is sucked via the suction muffler 70 from a suction pipe 15, compressed through the inside of the piston 30, and discharged through the discharge valve 62, the discharge cap 64 and the discharge muffler 66.
FIG. 2 shows the concrete configuration of the conventional suction muffler. In a case where the piston 30 existing on the inner diameter of the cylinder 20 is reciprocated, the suction muffler 70 fastened to the piston 30 sucks the refrigerant.
In detail, the suction muffler 70 includes a cylindrical muffler casing 72 of a relatively large diameter having an inlet and an outlet at front and rear ends in an axis direction to let refrigerant in and out, an inner suction pipe 73 installed inside the inlet 74 of the muffler casing 72, a vertical partition wall 76 for separating an inner space defined by the inside of the muffler casing 72 and the inner suction pipe 73, a horizontal partition wall 77 bonded to the vertical partition wall 76 to form the horizontal shape, and a cylindrical outer suction pipe 75 of a relatively small diameter installed outside the outlet of the muffler casing 72. Here, the refrigerant flows into the inlet 74 of the muffler casing 72, flows along the inner suction pipe 73, passes through the vertical partition wall 76 and the horizontal partition wall 77, and flows along the outer suction pipe 75.
The mass flow of the refrigerant passing through the conventional suction muffler can be better understood with reference to FIG. 3. The mass flow of the refrigerant passing through the outer suction pipe 75 has the same wave as that of an operating frequency of the linear motor. An inflow amount of refrigerant is larger or smaller than the average, which reveals the weakness in the performance of the conventional linear compressor.
As described above, since the amount of the refrigerant from the suction muffler is repeatedly smaller or larger than the average, the conventional linear compressor has a problem in supplying an efficient cooling force. Moreover, in order to supply a high cooling force, an excessive load is applied to a moving member for compressing refrigerant, which results in a short lifespan.